This is the combination of a donkey punch and a snowmobile. While the guy is ravaging the chick from behind (the chick is on all fours), he gives her a donkey punch. Right when she recieves the punch, the man uses his other arm to sweep the chick's arms out from underneath her in one smooth move. Then, much to her dismay, she falls.
While Joel was ravaging his new woman from behind, he pulled out his best move ever: the donkey mobile. This ensured that she was very confused, and it made him a proud man.